Helicopter rotor blades made of composite materials are known. In the following description and Claims, ‘composite material’ is intended to mean non-metal materials produced by combining a heat-setting resin matrix and a disperse phase comprising reinforcing, e.g. glass, carbon or graphite, fibres.
Composite materials have numerous advantages over conventional metal materials they have excellent mechanical properties in relation to versatility, durability and specific weight—which is normally lower than that of metal materials; are highly resistant to fatigue and corrosion; and are structurally much more reliable, i.e. failure due to crack formation takes a relatively long time, thus enabling anomalies to be detected more easily.
Known blades normally comprise a root portion connected to the rotor hub; and a main portion defining the body of the blade itself. Blades of this sort are usually made by forming, in successive stages, a main structure comprising a number of composite material components joined using adhesive, and which may be either structural components or fillers, i.e. low-mechanical-performance components. The structural components are made by depositing one or more layers of continuous (long) woven fibres, e.g. of carbon or glass, preimpregnated with resin; whereas, in the filler components, the fibres are discontinuous (short). All the components are made independently in respective polymerization stages, and then joined using adhesive to form the main structure.
The main structure is then covered with further layers of composite material, normally glass fibres preimpregnated with resin, to form the outer skin of the blade; and the whole so formed is then polymerized in a mold to the final configuration.
A need is felt within the industry for fabrication solutions by which to reduce the risk of local failure at the blade root spreading rapidly to the surrounding areas and resulting in complete detachment of the blade from the rotor.